A specific class of gyro may be identified in which polarity of the gyro bias is reversed when the drive and sense axes are interchanged. This particular class of gyro may be identified as Class II Coriolis Vibratory Gyro (CVG) and may be characterized by being inherently counterbalanced, symmetrical about the input axis and having orthogonal degenerate vibration modes. Self-calibration of the gyro bias with varying angular rate input may be achieved by employing two gyros to measure the angular rate and sequentially reversing the gyro bias. Self-calibration of gyro bias with constant angular rate input may be achieved with a single gyro in applications such as gyrocompassing for North finding. The sequence of data from the gyros may be processed in an algorithm to solve for the gyro biases and subtract them from the measured rate. The two self-calibrated gyro angular rate measurements are averaged to reduce the angle random walk.
Proof-of-concept testing of the Hemispheric Resonator Gyro (HRG) has demonstrated that, in the case of Class II Coriolis Vibratory Gyros (CVG), interchanging the drive and sense modes reverse the polarity of the gyro while keeping the gyro bias unchanged. This ability to electrically reverse the polarity of the gyro enables the direct observation of the gyro bias and allows the bias to be removed as an error source. In a static angular rate environment, such as gyro compassing in pointing applications, a single gyro may be used to determine orientation with respect to true north without the need to mechanically reverse the gyros sensing axis. In dynamic angular rate environments, such as a moving vehicle or aircraft, two gyros per axis with alternating polarities may be used to continuously derive the bias of each gyro and remove gyro bias as an error source in an inertial system's determination of position, velocity and orientation of the vehicle or aircraft. A similar approach has been proposed for the determination of accelerometer bias by alternating the position of the center of gravity of a proofmass to either side of a centerline of a suspension to reverse the polarity of the accelerometer.
Today, state-of-the-art micromachined vibrating gyroscopes operate at low frequencies (for example, 3-30 kHz) and rely on increase in mass and excitation amplitude to reduce noise floor and improve bias stability. It is desirable to reduce the flicker noise floor, or bias uncertainty of vibrating gyros without having to increase the mass and drive amplitude, which is difficult to achieve in low power and small size.